Timeline of Orlando nightclub shooting

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Photos:Orlando nightclub shooting

Police investigate the back of the Pulse nightclub in Orlando on Sunday, June 12. At least 49 people were killed there by Omar Mateen, who was shot and killed by Orlando police. It was the deadliest mass shooting in U.S. history.

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Photos:Orlando nightclub shooting

Bodies arrive at the medical examiner's office on June 12.

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Friends and family react after a list of hospitalized victims is released June 12 outside a hotel near the Orlando Regional Medical Center.

Police in Orlando direct family members away from the scene of the shooting.

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Shooting victims are attended to by emergency responders outside the club.

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Emergency personnel gather outside the nightclub.

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Bystanders wait at the scene.

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Police officers respond to the scene of the shooting.

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(CNN)Here's a timeline of the deadliest mass shooting in U.S. history, when a gunman killed 49 people and wounded 53 in the early morning hours of June 12 at Pulse nightclub in Orlando. This timeline is based on information provided by Orlando police Chief John Mina, SWAT Captain Mark Canty, Mayor Buddy Dyer, first responder dispatch, witness accounts, the FBI and other law enforcement authorities.

Gunshots shatter the night

Sunday, 1:58 a.m. ET: Some 320 people are enjoying a "Latin flavor" event at Pulse, a gay nightclub in the heart of Orlando. Clubgoer Patience Carter hears gunshots in the center section of the club shortly after she and friends agree to contact Uber for a ride home. They rush into a bathroom.

Around 2:02 a.m. ET: An officer working extra duty in uniform at the club hears gunshots and engages the shooter. The officer feels he is outgunned, retreats from the club, and calls for assistance. Two SWAT officers in a nearby patrol car are among units that respond and a gunbattle ensues.

Other patrol officers rush into the club during the shootout to pull survivors out.

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The shooter retreats and after exchanging gunfire with a SWAT lieutenant in a hallway he barricades himself and clubgoers in a bathroom.

Some 100 officers from the Orange County Sheriff's Office and the Orlando Police Department respond to the chaotic scene over the next 45 minutes.

Police say they receive communications from from clubgoers who say they are trapped inside the bathroom. This is when they say they knew there were hostages.

2:09 a.m. ET: Pulse posts an urgent message on Facebook: "Everyone get out of Pulse and keep running."

A tense standoff follows. Police later say they had to wait three hours to assess the situation, get armored vehicles on the scene and make sure they had enough personnel.

Approximately 2:22 a.m. ET: Shooter talks to 911 dispatch three times. He calls and hangs up. He calls and talks briefly. The dispatcher calls back. During the calls, the shooter pledges allegiance to ISIS. He also mentions the Boston Marathon bombers and a Florida man who died as a suicide bomber for al Nusra Front in Syria. Patience Carter says he also told a 911 dispatcher he wanted America to stop bombing his country. She said he started speaking a foreign language, probably Arabic, when he ended the call.

Approximately 2:45 a.m. ET: Killer calls News 13 Orlando and speaks to producer Matt Gentili. Shooter takes responsibility for the attack and claims he did it for ISIS. At some point, he also posts on Facebook.

2:49-2:51 a.m. ET: Justice texts his mother again:

--He;s in the bathroom with us

--women's bathroom is

--(mom) is the man in the bathroom wit u

--hes a terror

--yes

Justice was killed.

Approximately 2:30-5 a.m. ET: Hostage negotiators communicate with the shooter while he's barricaded in the bathroom. He threatens to put explosive vests on four hostages and to detonate the vests in 15 minutes. SWAT officers prepare for an explosive breach. During this time police do not exchange fire with the killer.

Officers continue to rescue people from inside the club while the gunman is in the bathroom.

While officers are negotiating with the suspect, eight people were able to escape with the help of law enforcement, by removing an air conditioning unit and crawling through the hole created.

Around 4 a.m. ET: The killer texts his wife and asks if she has seen the news, a source tells CNN.

Approximately 4 a.m. ET: Orlando's chief medical examiner, Dr. Joshua Stephany, receives a call about 11 or 12 casualties in the club. Soon after, he receives notification that the body count had reached 20, then 30. Stephany and his staff head to the nightclub.

Approximately 5 a.m. ET: SWAT members detonate an explosive to blow a hole in the wall but its only partially effective. They then use an armored vehicle to breach the final hole in the wall. But it leads them only to the hallway, not to the bathroom. They continue trying to breach using the vehicle.

They also smash down a door at the club, clearing the way for some 30 people inside to flee to safety.

12:03 p.m. ET: Gov. Rick Scott posts on Twitter: "This is an attack on our people. An attack on Orlando. An attack on Florida. An attack on America. An attack on all of us." He declares a state of emergency in Orange County.

This is an attack on our people. An attack on Orlando. An attack on Florida. An attack on America. An attack on all of us.

The shooter was a "person filled with hatred," Obama says. He also orders the American flag be lowered to half-staff at the White House and all other government buildings until sunset on June 16.

"In the face of hate and violence, we will love one another," Obama says. "We will not give in to fear or turn against each other, instead we will stand united as Americans to protect our people, to defend our nation, and take action against those who threaten us."